For horror and suspense writers, the most important chemical reaction is different: the scent of fear and hint of danger the hero detects that lets him react just in time to save his own life.

These may sound like cliches, but they’re based on real-life reactions our bodies have to pheromones.

Earlier this week I went to a lecture by Karl Grammar of the University of Vienna, one of the few scientists in the world studying human pheromones. He gave us an insight into how humans react to the scent of pheromones, and I thought some of it might be useful, or at least interesting, to my fellow writers.

Let me preface this by saying that I didn’t take notes on the scientific nitty-gritty, so some of what follows here may be educational while other parts will just sound strange. Take what you will and store it away – surely it’ll come in handy for a pub quiz one day.

What are pheromones?

Dr Grammar began by saying that in almost all animal species life is controlled by highly volatile substances made by the glands. These are pheromones. We breathe them in, and our olfactory system takes these scents (which we don’t even know we’re smelling) straight to the brain.

In other words, people give off these super subtle messages which our nose takes to our brain for interpretation.

What do pheromones help us do?

Pheromones help us do things like recognize our relatives, select our mates, and be aware when someone scary or aggressive is nearby.

We have hundreds – possibly thousands – of different pheromones. They’re transmitted through our skin; since we each have a unique genetic epidermal composition, our pheromones “smell” different. This makes it easier for us to identify our kin, but it also means romance novels are right: we can identify that one person who’s special to us, even if we can’t see them.

Humans have some of the same pheromones as other animals. For example, one of the pheromones men have is the same as a boar’s. Dr Grammar explained that when a female boar smells a male boar’s pheromones, she assumes the copulation position. “It doesn’t work like this for humans,” he said.

Women share a pheromone in common with wasps. Yep, women smell sorta like wasps, men smell like pigs, and no one knows why.

Also, the human egg produces a lily of the valley pheromone to attract sperm.

And women smell more attractive when they’re pregnant or lactating, but again researchers aren’t sure why.

Why sniffing sweaty shirts is good for science

Dr Grammar told us about several experiments helping scientists understand pheromones better. Most of the experiments focus on getting people to sniff sweaty t-shirts. Not experiments I’ll be signing up for anytime soon.

These aren’t just any sweaty shirts. People have to follow strict rules to minimize any chance of fragrances interfering with the scent of their pheromones. They can’t have sex, cigarettes, alcohol, garlic, cologne, or instant soups.

Dr Grammar: “We don’t get many students volunteering for these experiments.”

One experiment focused on the scent of beauty. Young men and women were shown pictures of the opposite sex and asked to rate the person’s attractiveness. Another group sniffed t-shirts and were asked to rate their attractiveness.

The result: attractive women smell attractive. Attractive men stink.

Dr Grammar said one possibility is that attractive men know they’re hot so they put less out physically because they don’t feel they have to.

The researchers looked further and discovered that ovulating women thought attractive males smelled pleasant. Basically, they were in do-me mode and the men’s pheromones sent them sexy messages. Women who weren‘t ovulating thought attractive men smelled unpleasant: get-the-hell-away-from-me-I’m-not-in-the-mood syndrome.

How we avoid having sex with relatives

You know that completely icky feeling you get at any hint of incest? That could be pheromones at work. Like I said earlier, because the “scent” of our pheromones is influenced by our genes, they help us detect people who are relatives.

Experiments have found that the pheromones of opposite sex kin repulse people. That’s your body’s way of saying, “Dude, she’s your sister! Gross!”

This partially explains the coronary my brother used to have when we were teenagers and our t-shirts would get mixed up in the laundry. Whenever he saw me wearing one of his shirts, he’d yell, “Take it off right now! You’re sweating in it!”

Experiments have also found that babies can identify their parents (but they associate more strongly with their mother). Apparently they can even identify breast pads worn by their own lactating mother over those worn by other women.

Pheromones help you find your mate

Just like they can tell you who not to sleep with, pheromones can help draw you to someone who’s genetically compatible.

Researchers in Switzerland gave women some men’s sweaty t-shirts to sniff and discovered they preferred men with immune systems that were completely different to theirs. But one year later, studies in the U.S. showed the exact opposite.

This could mean that when an environment is largely genetically homogeneous (like in Switzerland) people go for difference as a way of introducing diversity into the gene pool. When an environment is heterogeneous (like the U.S.), people are attracted to similarities.

The scent of loved ones can also be comforting. Research on couples found that when they separated the man and woman, women slept much better when researchers put the man’s t-shirt inside her pillow (without her knowing it was there).

Even though we are often considered visual creatures, Dr Grammar emphasized the importance of scent over sight: “You can look away, but you can’t smell away.”

At the end of the lecture, one guy raised his hand and asked what the point of kissing is, since it “serves no evolutionary purpose”.

Dr Grammar strenuously disagreed. He said it would be difficult to prove, but that kissing could be humans’ way of testing for immune-compatibility. Taste doesn’t really exist independent of smell, so we could be “tasting” (smelling) our potential mate’s pheromones.

Not really something to put in a romance novel: She parted her lips, her tongue darting out to stroke his taste receptors. Mmm…yes, he would provide her with strapping sons and wide-hipped daughters to carry on their genetic material.

Okay, that’s more than enough from me. What do you know about chemical attraction? Does knowing this kind of detail remove the “magic” from human lives, or does it add to the magic for you? Know any good pheromone stories? Do you like sniffing sweaty t-shirts?

This reminded me of one of the first dates I went on with my now husband of 42 years. I told him I liked his cologne. It wasn’t until months later that he told me he wasn’t wearing any at the time. I guess my nose knew lol.

I recently wrote a novel ” The Girl Who Lived With The Indians” and in my research of the Indian courtship I found that Indians could tell when a woman was sexually available to him by her smell of arousal. I also learned that they don’t perspire like we do, and they could tell a man was white by his smell. also being raised on a farm I learned that the male animal was continually smelling the female’s vulva area, but she would not accept him until she was ovulating. Evidently he knew she was close by her smell. We are animals so why would we be different?. .

I will always remember one of the first books I read when I moved from YA to adults included the zoologist character describing peanut butter on toast as human pheromones… and managing to make it sexy still with me over 10 years later.

I noticed that too. Even before me and my friend had fully recognized our feelings, I had unconsciously picked up on his scent. Later after I’d been through some particularly intense emotional turmoil, when we hugged and I buried my head into his shirt, I sniffed and inhaled his scent. And it helped comfort and calm me. When we kissed the first time, his scent was one of the things that attracted me to him and urged me into the kiss.